"To see the look on the faces of the kids as we were handling and weighing the toads and then euthanizing them was just...," Townsville City Councilman Vern Veitch said, breaking off to let out a contented sigh. "The children really got into the character of the event."

The toads — which can grow up to 8 inches in length — were imported from South America to Queensland in 1935 in a failed attempt to control beetles on sugarcane plantations. However, the toads couldn't jump high enough to eat the beetles, which live on top of cane stalks, and instead became pests themselves, their population booming because they have no natural predator.

The toads spread diseases, such as salmonella, and produce highly toxic venom from glands in their skin that can kill would-be predators. They are also voracious eaters, chomping up insects, frogs, small reptiles and mammals — even birds. Cane toads are only harmful to humans if their poison is swallowed.

Queensland politician Shane Knuth came up with the Toad Day Out idea. With each adult female cane toad capable of producing 20,000 eggs, he said, killing even a few thousand toads could ultimately wipe out millions.

On Saturday night, participants fanned out under the cloak of darkness to hunt down the toads. On Sunday, the toads — which the rules stated must be captured alive and unharmed — were brought to collection points and examined by experts to ensure they were not harmless frogs. The creatures were then killed, either by freezing or by being placed in plastic bags filled with carbon dioxide. Some of the remains will be ground into fertilizer for sugarcane farmers.

The Royal Society for the Prevention of Cruelty to Animals has applauded the effort, provided the toads are killed humanely.

In Townsville, organizers received around 3,600 toads from about 400 participants, said Andrew Hannay, coordinator of environmental management for Townsville City Council. Most of the toads will be donated to nearby James Cook University, with the biggest ones turned into souvenirs by local taxidermists, he said.

The largest toad weighed more than a pound, Mr Hannay said. His captor received several movie passes and a trophy made out of a cane toad.